A typical phase detector is shown in FIG. 1A. This phase detector is sometimes referred to as an Alexander phase detector, or a Bang-Bang phase detector. An analog signal received on line 102 is sampled by the flip-flop 106 on the rising edge of the clock signal on line 104. The analog signal is again sampled on the falling edge of the clock by the flip-flop 108. On the next rising edge of the clock signal, the analog signal is again sampled by flip-flop 106, while the previous samples are shifted into flip-flops 110 and 112. Thus, the data samples held in flip-flops 110, 112, 106 correspond to samples A, B, and C, respectively, as shown in FIG. 1B. If the outputs of flip-flop 106 and 110 are both the same (A=C), then the outputs of exclusive OR (XOR) gates 116, 120, are both equal to zero and no phase update occurs. On the other hand, the presence of either a falling edge (from high to low) or a rising edge (from low to high) in the data signal will result in different values for A and C (A≠C), and a phase update may be validated.
FIG. 2A shows an analog-to-digital converter (ADC) 200. As shown, the ADC 200 is a flash ADC. According to FIG. 2A, the ADC 200 includes voltage comparators 2061 to 2062N−1, with analog signal 202 and threshold voltages 2041 to 2042N−1, respectively, as inputs to the voltage comparators 2061 to 2062N−1. The outputs of each of the comparators 2061 to 2062N−1 are a digital word typically referred to as a thermometer code, and it may be present on a bus, buffer or register depicted as 208.
Each comparator 206 produces a “1” when the analog signal 202 is greater than its particular threshold voltage. Otherwise, the comparator output is “0”. Thus, if the analog input 202 is between threshold voltage 2042 and 2043, for example, voltage comparators 2063 to 2062N−1 produce “1”s and the remaining comparators (comparators 2061 and 2062) produce “0”s.
The thermometer code 208 shows the range of “1”s and “0”s in a plurality of bit slots. The point where the code changes from “1”s to “0”s is the point where the analog signal 202 becomes smaller than the threshold voltage for the respective comparator. The thermometer code 208 is referred to as such because of its similarity to a mercury thermometer, where a mercury column (i.e., “1”s) always rises to the appropriate temperature and no mercury (i.e., “0”s) is present above that temperature. The output of the thermometer code 208 is connected to decoder 212 via bus 210, and the output 214 of the decoder 212 is typically an N-bit digital code.
In some applications, the ADC may include a series of one or more buffers connected to each comparator. As shown in FIG. 2B, buffers 2071 to 207M are connected in series to comparator 2064, and each of the buffers 2071 to 207M are connected to clock 216 via lines 2161 to 216M. The buffers 2071 to 207M cooperatively store and shift comparison values generated by the comparator 2064.